Drop on demand inkjet technology has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an inkjet image is formed by the selective activation of inkjets within a print head to eject ink onto an ink receiving member. For example, an ink receiving member rotates opposite a print head assembly as the inkjets in the print head are selectively activated. The ink receiving member may be an intermediate image member, such as an image drum or belt, or a print medium, such as paper. An image formed on an intermediate image member is subsequently transferred to a print medium, such as a sheet of paper.
FIGS. 5A and 5B illustrate one example of a single inkjet 10 that is suitable for use in an inkjet array of a print head. The inkjet 10 has a body 22 that is coupled to an ink manifold 12 through which ink is delivered to multiple inkjet bodies. The body also includes an ink drop-forming orifice or nozzle 14. In general, the inkjet print head preferably includes an array of closely spaced nozzles 14 that eject drops of ink onto an image receiving member (not shown), such as a sheet of paper or an intermediate member.
Ink flows from manifold 12 through a port 16, an inlet 18, a pressure chamber opening 20 into the body 22, which is sometimes called an ink pressure chamber. Ink pressure chamber 22 is bounded on one side by a flexible diaphragm 30. A piezoelectric transducer 32 is secured to diaphragm 30 by any suitable technique and overlays ink pressure chamber 22. Metal film layers 34, to which an electronic transducer driver 36 can be electrically connected, can be positioned on either side of piezoelectric transducer 32.
A firing signal is applied across metal film layers 34 to excite the piezoelectric transducer 32, which causes the transducer to bend. Because the transducer is rigidly secured to the diaphragm 30, the diaphragm 30 deforms to urge ink from the ink pressure chamber 22 through the outlet port 24, outlet channel 28, and nozzle 14. The expelled ink forms a drop of ink that lands onto an image receiving member. Refill of ink pressure chamber 22 following the ejection of an ink drop is augmented by reverse bending of piezoelectric transducer 32 and the concomitant movement of diaphragm 30 that draws ink from manifold 12 into pressure chamber 22.
Typically, the layers of inkjet 10 are laminated metal plates or sheets. These sheets may be stainless steel, for example, that are chemically etched to form the structures and cavities in the plates that are then stacked to form the inkjet stack. Referring once again to FIGS. 4A and 4B, these sheets or plates include a diaphragm plate 40, an inkjet body plate 42, an inlet plate 46, an aperture brace plate 54, and an aperture plate 56. The piezoelectric-transducer 32 is bonded to diaphragm 30, which is a region of the diaphragm plate 40 that overlies ink pressure chamber 22.
Ink that flows through a print head may contain solid debris. This debris may be small enough to enter a manifold within a print head, but large enough to clog an inlet, an outlet, or an aperture. To address this issue, filter layers may be included in an inkjet ejector stack. These filters may be included in a channel layer to filter ink flowing into an inkjet ejector through an inlet. Typically, these filters are fabricated from stainless steel, nickel electroformed screens, woven mesh screens, or polyimide layers. The pores are required to be smaller in diameter than the final aperture through which the fluid passes so they block the passage of contaminants large enough to block the final aperture. Ancillary structure may also be provided to redirect fluid flow to another portion of the filter in the event that a portion of the filter becomes clogged.
A known goal of print head design is to increase the number of inkjet ejectors per unit of distance in a print head. As the number of inkjet ejectors per unit of distance increases, the size of the inkjet ejectors is reduced. Consequently, the fluid passageways in the inkjet ejectors become smaller and clean ink flowing in those passageways becomes increasingly important. Therefore, effective filtering of the ink continues to be an important factor in print head design.